The invention relates in particular to a process for the production of a honeycomb body using a hard metal sheet, especially for exhaust gas catalytic converters. The invention also relates to a semi-manufactured honeycomb body.
It is known for honeycomb bodies to be formed by stacking and/or winding sheet metal layers, at least some of which are structured sheet metal layers. Such honeycomb bodies are used, for example, as support bodies for catalytically active coatings.
In order to produce such a honeycomb body, at least one metal sheet is used, which is at least partially structured. The metal sheet or metal sheet portions is or are stacked and/or wound, in dependence on the structure of the honeycomb body. Different structural configurations of a honeycomb body as a catalytic carrier support body are described, for example, in European Patent Application 0 245 738 A1.
The honeycomb body is then subjected to a brazing material-coating operation. Thereafter the sheet metal layers are brazed together. The operation of brazing the sheet metal layers is implemented in particular in a vacuum brazing furnace.
It is known that honeycomb bodies of that kind are produced from metal sheets which have a thickness of about 110 xcexcm. It is known for the metal sheet to be subjected to a soft-annealing operation after the cold rolling operation so that a certain degree of elasticity is imparted to the metal sheet. Such elasticity ensures that the metal sheet can be provided with a structure, without the metal sheet suffering damage. The structures involved are in particular corrugation configurations which are formed in the metal sheet by way of suitable corrugating rollers. The fact that the metal sheet has been subjected to a heat treatment operation, the soft-annealing procedures, means that the shaping tools are also not subjected to an excessive loading.
It is also known (from a paper entitled xe2x80x9cThe Development and Application of a Metal Supported Catalyst for Porsche""s 911 Carrera 4xe2x80x9d by Stephan Pelters et al., in SAE Technical Paper Series 890488) that metal honeycomb bodies can be made from thin metal sheets or metal foils having a thickness of about 50 xcexcm. Such metal sheets have also been subjected to a soft-annealing operation.
It is accordingly an object of the invention to provide a process for producing a honeycomb body using a hard metal sheet and a semi-manufactured honeycomb body, which overcome the hereinafore-mentioned disadvantages of the heretofore-known methods and products of this general type and in which the expenditure involved in the production of the honeycomb body can be reduced, the semi-manufactured honeycomb body is easier to produce and the metal sheet is particularly suitable for the production of a honeycomb body.
With the foregoing and other objects in view there is provided, in accordance with the invention, a process for the production of a honeycomb body, in particular for an exhaust gas catalytic converter, which comprises at least partially producing a structure in at least one hard metal sheet having a thickness of at most 80 xcexcm by cold-shaping the at least one hard metal sheet without a previous soft-annealing; and layering and winding, or winding, the at least one at least partially structured hard metal sheet.
Surprisingly, it was found that on one hand, the nature of a hard metal sheet having a thickness of at most 80 xcexcm is such that it permits a cold shaping operation to be implemented to provide a structure without the hard metal sheet being excessively mechanically loaded by the cold shaping operation. On the other hand, it was also found that, when dealing with such a hard metal sheet, during a winding operation, the structure introduced into the hard metal sheet is substantially retained, which was not guaranteed when dealing with soft-annealed sheets having a small thickness. This is a matter of particular importance, especially in regard to the use of honeycomb bodies as exhaust gas catalytic converters. That is because in exhaust catalytic converters the flow passages that the honeycomb body has have a significant influence on the flow characteristics and therewith also on the catalytic performance of the exhaust gas catalytic converter.
The fact that the honeycomb body is formed from a hard metal sheet which is subjected to a cold shaping operation without previous soft-annealing provides that there is also a markedly lower degree of variation in the cell density. That is to be attributed to the fact that the structure of the hard metal sheet is retained in the winding operation, which is not the case when using a metal sheet which was subjected to a soft-annealing treatment prior to the cold shaping operation. A further advantage of the production process according to the invention is that it provides a honeycomb body which enjoys a higher level of brazing quality, after a brazing operation in which the hard metal sheets are joined together. By virtue of the fact that the hard metal sheet has a relatively high strength, the honeycomb body which is disposed in a layered configuration and wound, or merely wound, can be introduced into a tubular casing with a higher degree of prestressing than is the case when using metal sheets having a small thickness, which were subjected to a soft-annealing operation. Higher levels of contact forces between the hard metal sheets can be achieved by virtue of the higher level of prestressing effect. That is also the case even if a smooth metal sheet is introduced between two adjacent hard metal sheets.
It is known that, in order to provide a structure in a metal sheet, the metal sheet is prepared in the form of a winding or coil and the metal sheet is transported from the winding or coil by way of suitable transport rollers to a cold shaping station. In that case, the metal sheet is unwound from the winding or coil. The metal sheet is subjected to a tensile loading during the process of transporting it to and away from the cold shaping station. The process according to the invention for the production of a honeycomb body also achieves a reduction in stretching of the metal sheet when it is transported to and away from the cold shaping station. That is also the case during the operation of winding or coiling up the hard metal sheet.
In accordance with another mode of the invention, a hard metal sheet having a thickness of between 50 xcexcm and 80 xcexcm, preferably between about 60 xcexcm and 80 xcexcm, is subjected to an at least two-stage cold shaping operation. That alternative mode of implementation of the process provides that the tools for forming a structure which is, for example, a corrugation configuration that is produced in the metal sheet through the use of suitable corrugated rollers, are not exposed to an excessive loading or involve a low level of wear. A multi-stage cold shaping procedure also ensures that the hard metal sheet is not exposed to an excessive loading during the cold shaping operation thereof, so that the hard metal sheet is not damaged or destroyed.
In accordance with a further mode of the invention, a hard metal sheet having a thickness of at most 50 xcexcm, in particular 35 xcexcm, and preferably 20 xcexcm, is subjected at least in part to a cold shaping operation without a previous soft-annealing procedure. The hard metal sheet which has a thickness of at most 50 xcexcm is provided with a structure by the cold shaping operation, in such a way that the structure is formed in a one-stage cold shaping operation. In this case the cold shaping operation is implemented through the use of suitable tools of a tool profile which is also adapted to the thickness of the metal sheet.
In accordance with an added mode of the invention, in order to simplify the production of a honeycomb body which, for example, involves a honeycomb body wound in an S-shape, the hard metal sheet is divided into portions after the cold shaping operation, and the portions are disposed in a layered configuration and wound or coiled.
In accordance with an additional mode of the invention, at least one smooth metal sheet is disposed between two adjacent, at least partially structured metal sheets.
With the objects of the invention in view, there is also provided a semi-manufactured honeycomb body, comprising a tubular casing; and at least one at least partially structured hard metal sheet having a structure formed by cold-shaping without a previous soft-annealing, the at least one hard metal sheet having a thickness of at most 80 xcexcm, and the at least one at least partially structured hard metal sheet layered and wound, or wound, and disposed in the tubular casing.
Such a semi-manufactured honeycomb body is suitable in particular for forming an exhaust gas catalytic converter. That semi-manufactured honeycomb body can be subjected to continuing manufacturing procedures in further production steps. In particular, after a brazing material-coating operation it can be subjected to a brazing procedure. During the brazing procedure soft-annealing of the hard metal sheet can also take place so that possible non-homogeneities of the metal sheet can be eliminated by the actual brazing operation.
A semi-manufactured honeycomb body can be produced more economically by virtue of the fact that the hard metal sheet is subjected to a cold shaping operation without a previous soft-annealing procedure. In particular, the soft-annealing operation which involves a large amount of energy for carrying it into effect is not implemented in regard to the hard metal sheet.
In accordance with another feature of the invention, at least one hard metal sheet has a thickness of between 50 xcexcm and 80 xcexcm, preferably between about 60 xcexcm and 80 xcexcm, and the structure was formed by at least one two-stage cold shaping operation.
In accordance with a further feature of the invention, a hard metal sheet has a thickness of at most 50 xcexcm, in particular 35 xcexcm, and preferably 20 xcexcm, and the cold shaping operation can be effected in a one-stage procedure so that the structure is produced in the hard metal sheet in a single cold shaping step. The hard metal sheet provides a semi-manufactured honeycomb body which has reproducible passage cross-section sizes and shapes since the structure of the hard metal sheet is retained during the production of the semi-manufactured honeycomb body, by virtue of the properties of the material of the hard metal sheet.
In accordance with an added feature of the invention, there is provided at least one smooth metal sheet disposed between two adjacent, at least partially structured metal sheets.
With the objects of the invention in view, there is additionally provided a hard metal sheet for a honeycomb body, the hard metal sheet having a thickness of at most 80 xcexcm, and the hard metal sheet not previously subjected to a soft-annealing treatment.
Such a metal sheet enjoys strength adequate to ensure that when structures are formed in the metal sheet, they are not destroyed when the metal sheet is wound or coiled, for example to form a spiral honeycomb body. The use of the hard metal sheet also provides that, during production of the honeycomb body, no stretching of the hard metal sheet occurs upon transportation thereof to the cold shaping station and in the winding operation. This has the advantage of ensuring that the hard metal sheet was not so severely stretched prior to the cold shaping operation that crack formation within the hard metal sheet would occur due to the cold shaping operation. The avoidance of a stretching effect during an operation of winding the hard metal sheet also affords the advantage of retaining the structure which is produced in the hard metal sheet so that there is a markedly lesser degree of variation in the cell density in the case of a honeycomb body including the hard metal sheet according to the invention. Therefore, the use of the hard metal sheet means that the quality of the honeycomb bodies produced therefrom is consistent. In particular, the use of the hard metal sheet also means that the brazing quality can be improved since higher contact forces can be produced between the structures of the hard metal sheet and a smooth sheet metal layer, due to a suitable prestressing effect, during an introduction of the honeycomb body into a tubular casing.
In accordance with another feature of the invention, the hard metal sheet has a thickness of between 20 xcexcm and 80 xcexcm. In particular it is proposed that a hard metal sheet having a thickness of about 25 xcexcm be used to form a honeycomb body.
With the objects of the invention in view, there is furthermore provided an at least partially structured metal sheet for the formation of a honeycomb body, wherein the metal sheet has a thickness of at most 80 xcexcm. The metal sheet has not been subjected to a soft-annealing treatment.
The structure of the metal sheet can correspond to the structures which are known per se in the case of conventional honeycomb bodies. In particular the structure may involve a corrugation-type structure.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a process for producing a honeycomb body using a hard metal sheet and a semi-manufactured honeycomb body, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.